1. Technical Field
The present disclosure relates to a direct current to direct current (DC-DC) converting circuit, a display apparatus having the same and a method of driving the DC-DC converting circuit. More particularly, the present disclosure relates to a DC-DC converting circuit built in a display panel, a display apparatus having the DC-DC converting circuit and a method of driving the DC-DC con veiling circuit.
2. Discussion of Related Art
In general, a liquid crystal display (LCD) includes a liquid crystal display panel to display images and is classified into a polysilicon (poly-Si) LCD and an amorphous silicon (a-Si) LCD according to the type of thin film transistor included in the liquid crystal display panel.
In the case of the poly-Si LCD, a gate driving circuit that provides a gate signal to the liquid crystal display panel is built into the liquid crystal display panel and includes a polysilicon PMOS transistor. Meanwhile, a data driving circuit that provides a data signal to the liquid crystal panel is built into a driving chip mounted on the liquid crystal display panel as a chip-on-glass structure.
In a conventional driving chip, a timing controller, a memory and a DC-DC converting circuit are built into the driving chip together with the data driving circuit. In order to prevent a high voltage from being applied to the driving chip, however, a structure in which parts of the DC-DC circuit that generate a driving voltage for the gate driving circuit are built in the liquid crystal display panel has been developed.
In a conventional structure, a DC-DC converting circuit built into a liquid crystal display panel includes only polysilicon PMOS transistors in order to simplify the manufacturing process of the liquid crystal display panel. Such a conventional DC-DC converting circuit includes two polysilicon PMOS transistors, each of which has a diode-connected structure and a capacitor coupled to a clock signal to pump up a supplied voltage.
A voltage drop of an output voltage occurs due to a threshold voltage in the conventional DC-DC converting circuit, however, and the more the number of pumping circuits increases, the more the voltage drop of the output voltage increases. Moreover, electric power efficiency is about 50% or less, and the electric power efficiency becomes lower when the voltage level of the output voltage or the number of the pumping circuits increases.